1. Field of the Invention
The present invention generally relates to a semantic analysis method, a semantic analysis apparatus and a computer readable medium storing a semantic analysis program, and, more particularly, to the method, the apparatus and the computer readable medium in an information searching system used for an information providing service. The information searching system receives an inquiry information of a natural language sentence from a user, and carries out morphological analysis, syntax analysis and semantic analysis. As a result, a semantic structure is obtained. Then, the system extracts keywords as searching keys from the semantic structure, and infers a category name corresponding to the natural language sentence by using the keywords, and outputs a set of searching objects which belong to the category name.
2. Description of the Related Art
As a conventional example of the semantic analysis method, enhanced LINGOL has been proposed. The enhanced LINGOL generates the semantic structure by going back along the syntactic tree from a part of a speech node of the syntactic tree to a sentence (S) node which is a top node in a bottom-up manner.
The enhanced LINGOL includes semantic processing functions in each grammar rule which is used for syntax analysis. After the syntax analysis, the semantic processing functions are activated so as to carry out the semantic analysis. Shun Ishizaki, "Natural language processing", Shoukoudou, can be referred to for more information on this method.
However, in the information searching system which extracts keywords as searching keys from the semantic structure, each of the keywords to be extracted is a specific deep case of a verb in many cases. For example, the keywords to be extracted from an inquiry sentence, "I want to buy flowers in Tokyo", are a verb "buy", a commodity "flowers" and an address "Tokyo", the verb "buy" being the head of an infinitive phrase "to buy flowers in Tokyo" which is the objective case of a verb "want" which is the head of the sentence, the commodity "flowers" being the objective case of the verb "buy", and the address "Tokyo" being the location case of the verb "buy".
Thus, since deep cases which are necessary for extracting the keywords are determined in each information providing service session, it is unnecessary for extracting the keywords to obtain a semantic structure of the inside of the other deep cases.
In the conventional bottom-up search method, since semantic analysis of the inside of unnecessary deep cases is carried out, efficiency decreases and the time necessary for the semantic analysis increases.
In addition, in the method in which semantic processing functions are included in each grammar rule, since the semantic processing function needs to be made for each grammar rule, it is difficult to make the semantic processing function while grasping the whole flow of the semantic analysis.